Dear @Madhursr, Golden SunRise,
Yawning during meditation is very common, you need not worry about it or do not try to find a complex reason for it. Please understand, scientifically yawning occurs to balance the supply of oxygen in oneself. It generally happens when a body is tired due to fatigue mentally/physically or a working body is made to rest.
There is a minute difference between the two situations – Trance (Tandra) & Sleep (Nidra). While Nidra (sleep) is near to an unconscious situation, Tandra (Trance) is nearly Sleeping situation. In this position, several functions of the body are put to rest. Functions like sight, audition, olfaction (smelling), thoughts etc are at their minimal and gradually mandatory functions like heart beats & respiration goes down. Now being at this situation of rest, may induce yawning depending upon body to body.
In my opinion, it is in no case connected to your being fresh or tired. In fact, Sharat Sir, recommends that a deep meditation could be done better when a body is tired. Please go-ahead with your practice. May God bless.